Most individuals seeking to lose weight include increasing physical activity as part of their weight management strategy. For many, however, adding structured exercise does not result in the predicted amount of weight loss. Compensatory increases in energy intake and/or decreases in non-exercise physical activity appear to be significant factors limiting the effectiveness of exercise interventions. For each individual, the type and magnitude of these compensatory responses will predict the effectiveness of exercise to prevent weight gain or promote weight loss and, ultimately, cardiovascular health. Recent research has focused on the timing and magnitude of these compensatory changes in different population subgroups and across different intensities and durations of exercise. However, few studies have sought to identify the characteristics and traits that predict individual differences in the magnitude and direction of these compensatory behaviors. Accordingly, this study aims to: 1) identify psychological predictors of compensatory changes in diet and non-exercise physical activity in response to initiating a structured exercise program; 2) assess the relative importance of diet and activity changes in the total compensatory response; and 3) evaluate the influence of baseline body composition on compensatory changes in energy intake and expenditure. To meet these aims, a uniformity trial comprised of a series of four identical 8-week moderate-intensity walking interventions will be conducted in a community-based sample of 120 sedentary, premenopausal women (n=30 for each intervention). Psychological characteristics and traits known to be related to other health behaviors (e.g. smoking, substance abuse) will be assessed at baseline and compensatory changes in energy intake and energy expenditure will be measured over the course of the intervention. Multiple regression modeling will then be used to identify the psychological and physiological factors that explain substantial individual differences in compensatory behaviors among these women. Knowledge generated from this study will position the team to design a larger weight management intervention trial to explore the efficacy of a tailored approach that recognizes and attempts to manage identified psychological characteristics and traits among individuals differing in weight status. PUBLIC HEALTH RELEVANCE: While 150-250 minutes per week of moderate-intensity exercise is recommended for preventing weight gain and promoting modest weight loss, substantial inter-individual variability has been observed in the effectiveness of structured exercise to achieve expected levels of weight loss or maintenance. Compensatory behavioral changes in energy intake or non-exercise energy expenditure appear to be significant factors influencing the effectiveness of exercise interventions. This investigation will determine whether a number of plausible psychological and eating behavior traits predict these compensatory behavior changes - information that could subsequently be used to help tailor and target weight management interventions that include structured exercise.